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Updated: Aug 6, 2026
10:49
Measuring Rates of Herbicide Metabolism in Dicot Weeds with an Excised Leaf Assay
Published on: September 7, 2015
Herb-drug interactions: focus on pharmacokinetics
1PsychoFarmacology Consulting Services, College Park, MD, USA. alkaloid@jerrycott.com
CNS Spectrums
|August 31, 2004
Summary
St. John's wort (SJW) can lower drug levels by affecting cytochrome P450 (CYP) enzymes and P-glycoprotein (Pgp) pumps. This herb-drug interaction poses risks for medications metabolized by both systems.
Area of Science:
- Pharmacology and Pharmacognosy
- Drug Metabolism and Transport
Background:
- Herb-drug interactions are complex and require careful consideration.
- St. John's wort (Hypericum perforatum) is known to affect plasma levels of various drugs, including indinavir, cyclosporin, and digoxin.
- Existing knowledge of cytochrome P450 (CYP) metabolism alone does not fully explain these observed effects.
Purpose of the Study:
- To investigate the mechanisms behind St. John's wort (SJW) induced alterations in drug plasma levels.
- To highlight the role of P-glycoprotein (Pgp) in SJW-mediated drug interactions.
- To identify drug classes at particular risk due to combined CYP and Pgp substrate properties.
Main Methods:
- Review of recent literature on drug-drug, herb-drug, and food-drug interactions.
- Analysis of studies investigating the effects of St. John's wort (SJW) on drug metabolism.
- Examination of the impact of SJW on both cytochrome P450 (CYP) enzymes and P-glycoprotein (Pgp) transport.
Main Results:
- St. John's wort (SJW) has been shown to reduce plasma levels of several medications.
- Evidence suggests that SJW induces not only CYP metabolic pathways but also the P-glycoprotein (Pgp) transmembrane pump.
- The combined action of CYP 3A4 and Pgp induction by SJW presents a significant interaction risk.
Conclusions:
- St. John's wort (SJW) interactions extend beyond CYP metabolism to include P-glycoprotein (Pgp) induction.
- Medications that are substrates for both CYP 3A4 and Pgp require special caution when co-administered with SJW.
- Understanding these dual mechanisms is crucial for managing potential herb-drug interaction risks.
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